EP1317661A1

EP1317661A1 - Device for measuring exchanges of amounts of heat in non-stationary operating conditions

Info

Publication number: EP1317661A1
Application number: EP01962524A
Authority: EP
Inventors: Jean-Claude Padoy
Original assignee: Thermoflux SA
Current assignee: MAPE Sas
Priority date: 2000-09-11
Filing date: 2001-09-05
Publication date: 2003-06-11
Also published as: FR2813956B1; WO2002023144A1; FR2813956A1; US6817755B2; CA2421598A1; US20040042932A1

Abstract

The invention concerns a device (10) for measuring exchanges of amounts of heat in non-stationary operational conditions comprising an elongated housing (11) having one measuring end (12) closed and one connecting end (13) and a central cavity (14). The central cavity (14) contains a measuring cell (15) and electrical connection members (15). The housing (11) is extended by a hollow finger (17) which contains partly at least the measuring cell (15) which consists of a sensitive heat flux measuring element (18) sandwiched between a first heat conducting component (19) and a second heat conducting component (20). The contact surfaces of the heat conducting component (19, 20) are each coated with a gold film, so as to produce an intimate heat conducting bond with the sensitive heat flux measuring element (18).

Description

DEVICE FOR MEASURING EXCHANGES OF QUANTITIES OF HEAT IN NON-STATIONARY REGIME

Technical Field The present invention relates to a device for measuring the exchange of quantities of heat in a non-stationary regime, this regime having a low level dynamic embedded in an environment strongly disturbed by significant thermal fields, said device comprising an elongated housing provided with '' a central cavity, a measurement end and a connection end, the measurement end being closed and the central cavity containing, on the one hand, a measurement cell and, on the other hand, organs electrical connection, said measurement cell comprising at least one thermofluxmetric sensitive element sandwiched between a first thermally conductive part and a second thermally conductive part.

Prior art

Such a device makes it possible to measure in real time the quantities of heat generated during rheological modifications of materials being processed, such as for example synthetic materials during a plasticization process in an extrusion or injection machine. . The information collected is significant of the state of the material at a given instant, in particular of its pressure, its temperature, its viscous flow or, if necessary, its phase change, or its degradation during another transformation process.

It is known that data from sensors, in particular those relating to temperature, pressure and viscosity are capable of providing information on the state of matter, but it is complex to obtain, in real time, an complete local information on the rheological state of this material being transformed at a given time. We know from experience that all of this information can be supplied by so-called heat flow sensors by means of appropriate computer processing of the signals delivered by these sensors. The physical quantities previously stated all result in exchanges of quantities of heat, that is to say that any rheological phenomenon whose evolution can be reduced to a thermal quantity is detectable.

Most of the existing thermal flux sensors have been created to mainly measure fluxes of the thermal balance type representative of the thermal exchanges between matter and its environment. The heat fluxes generated within the material during local rheological modifications being very weak compared to the fluxes resulting from the exchanges with the environment, they are thus drowned in an important signal of level which it is necessary to process to be able to extract information from it sought. This is a cumbersome and expensive method and it appears complex to routinely integrate such devices in an industrial process for performing online control.

However, in this type of application, it is the dynamics of the transformations of the material which is essential and not the thermal balance. This is why a thermofluxmetric sensor has been developed which meets these requirements and which was the subject of the international patent application published under the number WO 00/08431 and having the title: Device for measuring the exchange of heat quantities in variable, non-stationary or transient regime.

This device comprises a measurement cell comprising at least one thermofluxmetric sensitive element sandwiched between a first thermally conductive part and a second thermally conductive part. The measuring cell has a flat circular base which is held in contact by mechanical compression means against the inner surface of the bottom of a body in which the measuring cell is arranged. As a result, the two parts which sandwich said sensitive element are in direct contact with the body of the device which is itself linked to the environment of the material to be checked. As a result, this device is designed to measure the exchange of heat quantities between the material to be checked and its immediate environment. By way of example, the device is capable of measuring the exchanges of quantities of heat between the sheath of an injection machine and the synthetic material itself being processed, which circulates inside this sheath in melted area. It is obvious that heat exchanges take place permanently between the material and its immediate environment so that the measurements carried out by this device do not make it possible to effectively and reliably control the evolution of the material being plasticized in the zone molten.

Statement of the invention

The present invention proposes to remedy these drawbacks by making it possible to carry out a precise control of the evolution of the material being transformed by a simple measurement of exchanges of heat quantities corresponding either to the exchanges due to the flow resulting from the thermal balance between the material and its environment, but exclusively for local exchanges between the material and a reference thermal element.

This object is achieved by the device as defined in the preamble and characterized in that said first thermally conductive part is in contact with at least one surface of said housing, and in that said second thermally conductive part is isolated from said housing and constitutes a capacity constant thermal.

Therefore, the sensitive element of the thermofluxmetric type is disposed between said first part, which constitutes a thermal electrode in contact with the medium to be checked, and said second part, which constitutes a determined thermal capacity. By these means, exchanges of heat quantities are measured, no longer between the material to be checked and its immediate environment, but between the material to be checked and a perfectly determined reference thermal capacity, integrated into the measurement cell and thermally isolated from the device housing.

When there is a local rheological modification within the material resulting in absorption, restitution or production of energy in thermal form, quantities of heat are exchanged with the thermal capacity of the measuring device by crossing the thermofluxmetric sensitive element. The quantities of heat are stored in the thermal capacity of the device, the temperature of which rises until it is balanced with that of the local matter.

When the phenomenon is no longer exothermic but endothermic, the thermal capacity of the device destocks, in the opposite direction, the quantities of heat which are exchanged with the material by crossing the thermofluxmetric sensitive element, and this until the next local thermal equilibrium.

The dynamics of these local heat exchanges are detected by the thermofluxmetric sensitive element which generates a significant electrical signal of these exchanges, and this in real time.

The electrical signal obtained is non-stationary. It provides information, in real time, on the dynamics of local rheological modifications of matter, and this in an environment strongly disturbed in particular by exchanges of thermal energy at very high level between matter and its environment.

According to a preferred embodiment, the measurement end of the housing is substantially flat and one of the ends of said first part thermally conductive is at least partially in contact with an interior surface of said measurement end.

Advantageously, said first thermally conductive part comprises a heel provided with a contact surface whose geometry corresponds to that of an interior surface of said measurement end.

According to a first embodiment, said contact surface of said heel of said first thermally conductive part is circular.

According to a second embodiment, the measurement end of the housing is substantially frustoconical and one of the ends of said first thermally conductive part is at least partially in contact with an interior surface of said measurement end.

In the context of this second embodiment, said first thermally conductive part comprises a heel provided with a contact surface, this contact surface being in abutment against an interior surface of the same geometry of said frustoconical measurement end.

Preferably, the thermofluxmetric sensitive element as well as said first thermally conductive part and said second thermally part are coated with a layer of gold, at least on their common surfaces, so as to ensure by diffusion of the layer of gold intimate thermal contact between the components concerned.

According to a particularly simple, efficient and advantageous construction, the housing comprises, on the side of its measurement end, a hollow finger whose thickness is reduced compared to that of the rest of the body so as to have a high axial thermal resistance, the cell being essentially housed in this finger. The measuring cell is preferably held at the bottom of the hollow finger by compression means arranged to ensure that said first thermally conductive part is pressed against the internal surface of the measuring end.

In a very interesting manner for constructive and functional reasons, the cross section of the hollow finger is circular, said first thermally conductive part has a semi-cylindrical section whose diameter is substantially equal to the diameter of the interior surface of the hollow finger, and the second thermally conductive part has a semi-cylindrical section whose diameter is less than the diameter of the interior surface of the hollow finger.

Brief description of the drawings The present invention will be better understood with reference to the description of various embodiments and the appended drawings, given by way of nonlimiting examples, in which:

FIG. 1 represents a view in partial longitudinal section of a first embodiment of the invention of the device according to the invention,

FIG. 2A represents an enlarged partial view in longitudinal section of the measurement end of the device of FIG. 1,

FIG. 2B represents an enlarged partial view in cross section along the line l-l, of the measuring end of the device of FIG. 1,

FIG. 3 represents a view in longitudinal section of a second embodiment of the device according to the invention,

FIG. 4A represents an enlarged partial view in longitudinal section of the measurement end of the device of FIG. 3, FIG. 4B represents an enlarged partial view in cross section, along line 11-11, of the measurement end of the device of FIG. 3,

FIG. 5 represents a view in longitudinal section of a third embodiment of the device according to the invention,

FIG. 6 is an enlarged partial view of the measurement end of the device in FIG. 5, and

- Figures 7A and 7B show views respectively from above and in longitudinal section of the thermofluxmetric sensitive element of the measurement cell housed in the measurement end of the device of the invention.

Ways to realize the invention

With reference to FIGS. 1, 2A and 2B, the device 10 according to the invention comprises a housing 11 of elongated shape which has a closed measurement end 12, a connection end 13 as well as a central cavity 14. This central cavity 14 contains, on the one hand, a measurement cell 15 and, on the other hand, electrical connection members 16. The housing 11 is extended, on the side of the measurement end 12, by a hollow finger 17, of section advantageously circular, which partly contains at least said measurement cell 15.

This measurement cell 15 consists of a thermofluxmetric sensitive element 18 which is sandwiched between a first thermally conductive part 19, which constitutes a kind of thermal electrode, and a second thermally conductive part 20, which constitutes a constant thermal capacity. called the reference thermal capacity. The contact surfaces of the first thermally conductive part 19 and the second thermally conductive part 20 are each coated with a layer of gold, so as to form an intimate thermal connection with the element. thermofluxmetric sensitive 18. The two thermally conductive parts 19 and 20 are linked together by screws 21 made of a thermally poorly conductive material.

In the embodiment described and represented by the figures, said first thermally conductive part 19 has a substantially semi-circular section and is provided at its free end with a heel 19a of substantially circular section which has a flat surface 19b of shape circular bearing on the interior surface 17a of the hollow finger 17. The diameter of this heel is less than or equal to the interior diameter of said hollow finger 17. Similarly, the diameter of said first thermally conductive part 19 is less than the interior diameter of said finger hollow 17 so that this part has no direct contact with the body of the finger. The only contact between said first thermally conductive part 19 and the hollow finger 17 is indirect and takes place via the surface 19b of the heel 19a.

A thermal insulator 22 is mechanically fitted onto the first thermally conductive part 19 thus ensuring the mechanical connection between the measurement cell 15 and the connection members 16 of the device as well as good thermal insulation of said measurement cell.

A hollow sheath 23, of cylindrical shape, made of an electrically insulating material, acts as an intermediate piece between the thermal insulator 22 and a braid clamp 20 of a two-wire cable 25. Two electrically insulating clamping terminals 26a and 26b are respectively disposed on either side of the thermofluxmetric sensitive element 18 and each have a wedge-shaped recess 27 in which is engaged one end of each electrically conductive wire or braid of the two-wire cable 25, applied against a face of the thermofluxmetric sensitive element 18 which comprises on each of its faces an appropriate electrically conductive track. The sensitive element thermofluxmetric 18 is sandwiched between the two electrically insulating clamping terminals 26a and 26b and held by means of two clamping screws 28 which ensure the clamping of said terminals by crushing between them the two electrical wires of the two-wire cable 25 on the electrical tracks of the thermofluxmetric sensitive element 18.

The braid clamp 20 takes support, at its end, on the hollow sheath 23 and has a cylindrical central bore allowing the passage of the conductive wires or the braid of the cable 25. The other end is arranged to operate a coaxial clamping of the braid with the sheath of the cable 25 when a clamping sleeve 29 is screwed to the connection end 13 of the housing 11 and this bushing compresses the clamping clamp 24.

The housing 11 is provided with a shoulder 30 which serves to support a tightening nut 31 split longitudinally and which extends substantially over the entire length of the said housing 11. This nut is intended to provide a mechanical connection with a support ( not shown) which is linked to the environment of the medium to be checked, for example to the sleeve of an extrusion press. The clamping nut 31 is externally provided with a thread which cooperates with the thread of said support linked to the environment of the medium to be checked.

Figures 3, 4A and 4B show views similar to those of Figures 1, 2A and 2B, they correspond to a second embodiment of the device according to the invention. Similar components will have the same reference numbers and will not be described in detail. Only the components which differ from those of the previous figures will be detailed.

In this embodiment, said first thermally conductive part 19 is not extended by a heel which ensures contact with the end of the hollow finger 17, but the part itself extends to the end of this hollow finger and comprises, at its end, a flat surface 19c, in the form of half disc, which bears against the interior surface 17a of the hollow finger 17. In addition, the diameter of said first thermally conductive part 19 is equal to the interior diameter of the hollow finger 17, so that the contact between this part and the body the hollow finger is made directly with the free end of the part and with its lateral surface 19d.

Figures 5 and 6 illustrate a third embodiment of the device according to the invention. Components similar to those of the previous figures and in particular of Figures 1, 2A and 2B will bear the same reference numbers and will not be described in detail. Only the components which differ from those of the previous figures will be detailed.

In this embodiment, only the end of the hollow finger 17 differs from that of the finger illustrated in Figure 1. The hollow finger is extended by a frustoconical end piece 31 which is arranged to be engaged in a suitable bore of a part in connection with the medium to be checked. The frustoconical shape of the end piece makes it possible to increase the contact surface between the hollow finger 17 and the part in contact with the medium to be checked and thus to obtain greater sensitivity and greater reliability of the measurements.

The heel 19a can be replaced by an extension of said first thermally conductive part 19, as is the case in the embodiment illustrated in FIG. 3. In addition, this heel can have a diameter equal to the inside diameter of the hollow finger 17, so as to increase the contact surface of said first thermally conductive part 19 with the body of the hollow finger.

FIGS. 7A and 7B represent the thermofluxmetric sensitive element of the measurement cell 15, respectively seen from below and seen in longitudinal section. This element comprises a thermofluxmetric detector 40, disposed between a first insulating layer 41 and a second insulating layer 42 which extend beyond the detector towards the end of connection. On the side of the measurement end, the two insulating layers 41 and 42 defined above are respectively surmounted by a first copper mass 43, called the absorption electrode, and a second copper mass 44, called the electrode of dissipation. On the side of the connection end, the two insulating layers 41 and 42 are separated from a third central insulating layer 45 by two conductive tracks, respectively 46 and 47. Two pass-through holes 48 and 49 are provided on the side of the end of measurement to enable the thermofluxmetric sensitive element 18, said first thermally conductive part 19 and said second thermally conductive part 20 to be connected by screws.

The device according to the invention is applicable to the measurement of the exchange of quantities of heat in a totally non-stationary regime comprising a low level dynamic embedded in an environment strongly disturbed by significant thermal fields.

In practice, the measuring end, the base of which is flat, as shown in particular in FIG. 2A, is usually engaged in a through bore so that this base is in contact with the material to be checked. The measuring end, the base of which is frustoconical, as shown in particular in FIG. 6, is preferably engaged in a blind bore, the end of which has the shape of a cone, the top of which is disposed at a short distance from the passage of the material to be checked.

In the first case, the sensor body, and more particularly the wall of this body located at the base of the measurement end, must withstand significant pressures, which can reach 2500 bars. In addition, the space between the body of the sensor and the wall of the through bore is invaded by material, in particular by plastics, which, by hardening, block the sensor in the bore and prevent its dismantling. Cold. In the second case, the sensor body is no longer in contact with the material, and is no longer subjected to the significant pressure of the latter. It can be dismantled at any time during the operation of an extrusion press, for example. As the distance between the measuring end and the material to be checked is small, thermal information is easily transmitted, all the more since the frustoconical shape makes it possible to increase by a factor of up to four the surface which captures variations in heat flux. The contact between the frustoconical base surface of the measuring end and the conical surface of the point of the bore is easy to achieve, which makes it possible in the second case to obtain a result identical, or even better than that 'is obtained in the first case, despite increased thermal resistance.

Possibilities of industrial applications As examples, this device can be advantageously used for:

-. online control of "crosshead" type extrusion heads so as to better optimize production by piloting based on rheological parameters of the states of matter, especially during complex extrusions, for example cables. -. the control of the stretch-blow molding molds, so as to better optimize the production by piloting based on the control of the crystallization of the material, especially during the production of synthetic bottles. -. control of the different phases of injection of thermoplastic materials into a mold, so as to improve quality, reduce cycle time and better control the injection process by better knowledge of different parameters such as pressure dynamics, l arrival of matter, detection of incomplete, crystallization reactions. -. control of the injection phases of thermosetting materials in SMC (Sheet Molding Compound) and BMC (Bulk Mounting Compound) compression molds so as to better optimize production by better controlling rheological parameters, especially during the crosslinking. -. the control of the degradation of greases used in particular in highly stressed bearings, under heavy load and at very high speed in order to optimize predictive maintenance.

The tests demonstrated the reliability and reproducibility of the signals delivered and in particular a remarkable dependence of the dynamic profile of thermal flux with those of the pressure. A series of these devices installed on a screw / sleeve system of an injection molding machine shows that such a thermomechanical signature has never been obtained to date, in particular in the molten zone, which gives hope for significant progress in knowledge. and online and real-time control of injection processes.

Claims

1. Device for measuring the exchange of quantities of heat in a non-stationary regime, this regime having a low level dynamic embedded in an environment highly disturbed by significant thermal fields, said device comprising an elongated housing (11) provided with a central cavity (14), a measurement end (12) and a connection end (13), the measurement end (12) being closed and the central cavity (14) containing, on the one hand, a measurement cell (15) and, on the other hand, electrical connection members (16), said measurement cell comprising at least one thermofluxmetric sensitive element (18) sandwiched between a first thermally conductive part (19) and a second thermally conductive part (20), characterized in that said first thermally conductive part (19) is in contact with at least one surface of said housing (11) and in that said second thermally conductive part nductrice (20) is isolated from said housing and constitutes a constant thermal capacity.

2. Device according to claim 1, characterized in that the measuring end (12) of the housing is substantially planar, and in that one of the ends of said first thermally conductive part (19) is at least partially in contact with an inner surface (17a) of said measuring end.

3. Device according to claim 2, characterized in that said first thermally conductive part (19) comprises a heel (19a) provided with a contact surface whose geometry corresponds to that of the interior surface (17a) of said end of measured.

4. Device according to claim 3, characterized in that said contact surface of said heel (19a) of said first thermally conductive part (19) is circular.

5. Device according to claim 1, characterized in that the measuring end of the housing (12) is substantially frustoconical, and in that one of the ends of said first thermally conductive part (19) is at least partially in contact with an inner surface of said measuring end.

6. Device according to claim 5, characterized in that said first thermally conductive part (19) comprises a heel provided with a contact surface, this contact surface being in abutment against an interior surface of the same geometry of said measurement end truncated.

7. Device according to claim 1, characterized in that the thermofluxmetric sensitive element (18) as well as said first thermally conductive part (19) and said second thermally conductive part (20) are coated with a layer of gold, at less on their common surfaces.

8. Device according to claim 1, characterized in that the housing (11) comprises, on the side of its measurement end (12), a hollow finger (17) whose thickness is reduced compared to that of the rest of the body of said housing, the measurement cell (15) being essentially housed in this finger.

9. Device according to claim 8, characterized in that the measuring cell (15) is held at the bottom of the hollow finger (17) by compression means arranged to ensure that said first thermally conductive part (19) is pressed against the inner surface of the measuring end (12).

10. Device according to claim 8, characterized in that the cross section of the hollow finger (17) is circular, in that said first thermally conductive part (19) has a semi-cylindrical section whose diameter is substantially equal to the diameter of the inner surface of the hollow finger and in that the second thermally conductive part (20) has a semi-cylindrical section whose diameter is less than the diameter of the interior surface of the hollow finger.

11. Device according to claim 8, characterized in that the thermofluxmetric sensitive element (18) comprises a thermofluxmetric detector (40) sandwiched between a first insulating layer (41), associated with an absorption electrode (43), and a second insulating layer (42), associated with a dissipation electrode (44).